Sputtering is widely used for the deposition of thin layers onto substrates. The process is carried out in a vacuum chamber which is filled with a chemically inert gas, ions of which bombard the target, transfer their momentum to the target material and cause particles of the material to be ejected from the target surface. Accordingly, after substantial use, the target material becomes eroded in a generally annular section of the target face, known as the target raceway.
In a conventional sputter target assembly, the target is attached to a support tube which is water-cooled to carry away the heat generated by the ion bombardment of the target. To prevent the coolant from escaping into the vacuum chamber, the connection between the target and the backing tube must be impervious to the pressure of the coolant and the vacuum. As the target surface is eroded by ion bombardment, there is increased danger of the target failing at the target raceway and allowing coolant to escape into the vacuum chamber. Therefore, sputtering targets must be replaced frequently.
Previously, aluminum targets were electron beam-welded to the support tube. The electron beam welding requires oversized targets and support tubes. The electron beam weld is an autogenous weld and therefore substantial amounts of the aluminum target and tube are melted in order to join the target to the support tube. Once the target has been welded to the tube, substantial machining is required to bring the oversized targets and tubes into the final shape. The melting of the aluminum during the E-beam welding and the subsequent machining of the target and support tube makes the fabrication of an entirely new target assembly, including both the target and the tube, necessary. Thus, each new target includes the cost of fabricating the support tube and of the machining.
Accordingly, it is an object of the invention to provide a reusable sputtering target support tube and an inexpensive method of reusing the support tube that does not require the post-bonding machining required when the prior art electron beam welding method is used.